The main objective of this research is to develop a markedly improved diagnostic test for the early detection of occult hemaglobin in stools of patients. Colon and rectal cancer has surpassed lung cancer as the number one cancer killer in the United States. Most investigators feel that occult bleeding is the most frequent consequence and most predictive indicator of the presence of tumor. The high mortality rate of near 60% makes the development of a diagnostic test for this cancer of extreme importance since early detection is associated with high cure rates. A number of tests have been developed to detect occult hemaglobin in stools. These include the dilute tincture of guaiac, saturated guaiac, Hemastat, and Hemoccult test. In addition, the punch-disc radial immunodiffusion technique has been developed and has demonstrated greater sensitivity than the previously mentioned tests as well as a degree of specificity not found in the previous tests. We will develop a punch-disc enzyme-linked immunosorbent assay (ELISA) for the detection of occult hemaglobin in stools. The sensitivity of the assay should be clearly superior to that of existing tests. Because of its greater sensitivity, the punch-disc ELISA will allow detection of hemaglobin antigens at an earlier stage of colon cancer development than the previously mentioned tests. An increased survivor rate should result from the earlier detection of colon cancer. This newly developed punch-disc ELISA will be evaluated critically in terms of standardization, sensitivity, specificity, and reproducibility. These characteristics are essential to the quality control of the assay. The findings in Phase I of this study will be used to plan the demonstration in Phase II of the practical application of the punch-disc ELISA as a diagnostic technique for the early detection of colon cancer and other causes of alimentary tract bleeding. The detection of bleeding from noncancerous lesions could be an important aid in the cure-rate of these lesions. The punch-disc ELISA is a specific, sensitive, accurate, and simple screening procedure that can be of significant value to practitioners, clinics, and other laboratories as a quantitative assay capable of detecting hemoglobin antigen in the nanogram range. As a colorimetric assay, the ELISA offers the advantage of being adaptable to a simple and inexpensive office and home test. (2)